The use of wireless networks has increased dramatically over the past few years. Wireless local area networks (“WLANs”) are now commonplace in the modern workplace. A WLAN offers several advantages over regular wired local area networks (“LANs”). For example, users are not confined to specified locations previously wired for network access, wireless work stations are relatively easy to link with an existing LAN without the expense of additional cabling or technical support; and WLANs provide excellent alternatives for mobile or temporary working environments.
In general there are two types of WLANs, independent and infrastructure WLANs. The independent, or peer-to-peer, WLAN is the simplest configuration and connects a set of personal computers with wireless adapters. Any time two or more wireless adapters are within range of each other, they can set up an independent network. In infrastructure WLANs, multiple access points link the WLAN to the wired network and allow users to efficiently share network resources. The access points not only provide communication with the wired network, but also mediate wireless network traffic in the immediate neighborhood. Both of these network types are discussed extensively in the IEEE 802.11 standard for WLANs.
In the majority of applications, WLANs are of the infrastructure type. That is, the WLAN typically includes a number of fixed access points, also known as base stations, interconnected by a cable medium to form a hardwired network. The hardwired network is often referred to as a system backbone and may include many distinct types of nodes, such as, host computers, mass storage media, and communications ports. Also included in the typical WLAN are intermediate base stations which are not directly connected to the hardwired network.
These intermediate access points, often referred to as wireless base stations, increase the area within which access points connected to the hardwired network can communicate with mobile terminals. Associated with each access point or base station is a geographical cell. A cell is a geographic area in which an access point has sufficient signal strength to transmit data to and receive data from a mobile terminal with an acceptable error rate. Unless otherwise indicated, the term access point or base station, will hereinafter refer to access points hardwired to the network and wireless base stations. Typically, the access point connects to the wired network from a fixed location using standard Ethernet cable, although in some cases the access point may function as a repeater and have no direct link to the cable medium. Minimally, the access point receives, buffers, and transmits data between the WLAN and the wired network infrastructure. A single access point can support a small group of users and can function within a predetermined range.
In general, end users access the WLAN through WLAN adapters, which are commonly implemented as PCMCIA cards in notebook computers, ISA or PCI cards in desktop computers, or fully integrated devices within hand-held computers. WLAN adapters provide an interface between the client network operating system and the airwaves. Typically, the nature of the wireless connection is transparent to the network operating system.
In general operation, when a mobile terminal is powered up, it “associates” with an access point through which the mobile terminal can maintain wireless communication with the network. In order to associate, the mobile terminal must be within the cell range of the access point and the access point must likewise be situated within the effective range of the mobile terminal. Upon association, the mobile unit is effectively linked to the entire LAN via the access point. As the location of the mobile terminal changes, the access point with which the mobile terminal was originally associated may fall outside the range of the mobile terminal. Therefore, the mobile terminal may “de-associate” with the access point it was originally associated to and associate with another access point which is within its communication range. Accordingly, WLAN topologies must allow the cells for a given access point to overlap geographically with cells from other access points to allow seamless transition from one access point to another. One example of this “association” process is described extensively in IEEE 802.11.
It is common practice for most “association” algorithms to primarily rely on the signal strength between the client and the access point to determine whether to establish a communication link. However, there a drawbacks associated with relying solely on the signal strength parameter. Such drawbacks include inefficient use of bandwidth, high network latency and failure to account to for interference between clients and access points.
The present invention addresses these and other problems encountered in the prior art, to provide a system for increased throughput over a broad range of network topologies and conditions.